Hydrocracking process

ABSTRACT

A PROCESS FOR HYDROCRACKING LUBRICATING OIL STOCKS TO LUBRICATING OILS OF HIGHER VISCOSITY INDEX IN WHICH THE PORTIONS OF A CRUDE SUITABLE FOR HYDROCRACKING ARE FRACTIONATED INTO A PLURALITY OF FRACTIONS COMMENSURATE WITH THE BOILING POINT, MOLECULAR WEIGHT, OR POLYFUSED-RING AROMATIC CONTENT AND EACH OF SAID FRACTIONS IS SUBJECTED TO HYDROCRACKING CONDITIONS COMMENSURATE WITH THE POLYFUSED-RING AROMATIC CONTENT OVER A HYDROCRACKING CATALYST AT A TEMPERATURE IN THE RANGE OF ABOUT 650* TO 875* F. AND A HYDROGEN PARTIAL PRESSURE OF AT LEAST ABOUT 1500 P.S.I. PREFERABLY, THE CHARGE STOCK S FRACTIONATED INTO THREE FRACTIONS, THE FIRST FRACTION BOILING IN THE RANGE OF ABOUT 650* TO 850*F., THE SECOND FRACTION BOILING IN THE RANGE OF ABOUT 850* TO 1000*F., AND THE THIRD FRACTION CONTAINING ALL THE MATERIAL BOILING ABOVE ABOUT 1000* F. WHICH HAS BEEN DEASPHATED; AND EACH OF THE FOREGOING FRACTIONS IS SEPARATELY HYDROCRACKED FOR AT LEAST A PORTION OF THE TOTAL TIME IT IS HYDROCRACKED, PREFERABLY OVER A HYDROCRACKING CATALYST COMPRISED OF A SULFIDE OF A GROUP VI METAL, LEFT-HAND COLUMN, AND/OR AN IRON GROUP METAL, AND   MOST PREFERABLY A MIXTURE OF NICKEL SULFIDE AND TUNGSTEN SULFIDE IN A 1/1 TO 4.&#39;&#39;1 METAL ION RATIO, AT A TEMPERATURE IN THE RANGE OF ABOUT 735* TO 825*F. AND A HYDROGEN PARTIAL PRESSURE OF ABOUT 2500 TO ABOUT 4000 P.S.I.

May 18, 1971 A. T. OLENZAK ET AL ,4

HYDROCRACKING PROCESS 2 Sheets-Sheet 2 Filed June 20, 1968 N mEDOE xuokw .rIwEm NO, 4 DIsTILLATE Q FRACTIONATOR n 02 Of NO. 2 DlSTlLLATE FRACT IONATOR NO. I DlS'lLLATE FRACTIONATOR INVENTORS ALBERT T. OLENZAK SHELDON L. THOMPSON ATTORNEY NO. I

moOmm OF 00mm mm m 0009 O. 00mm mm DEASPHALTER United States Patent O US. Cl. 208-59 9 Claims ABSTRACT OF THE DISCLOSURE A process for hydrocracking lubricating oil stocks to lubricating oils of higher viscosity index in which the portions of a crude suitable for hydrocracking are fractionated into a plurality of fractions commensurate with the boiling point, molecular weight, or polyfused-ring aromatic content and each of said fractions is subjected to hydrocracking conditions commensurate with the polyfused-ring aromatic content over a hydrocracking catalyst at a temperature in the range of about 650 to 875 F. and a hydrogen partial pressure of at least about 1500 p.s.i. Preferably, the charge stock is fractionated into three fractions, the first fraction boiling in the range of about 650 to 850 F., the second fraction boiling in the range of about 850 to 1000 F., and the third fraction containing all the material boiling above about 1000 P. which has been deasphalted; and each of the foregoing fractions is separately hydrocracked for at least a portion of the total time it is hydrocracked, preferably over a hydrocracking catalyst comprised of a sulfide of a Group VI metal, left-hand column, and/ or an iron group metal, and most preferably a mixture of nickel sulfide and tungsten sulfide in a 1/ 1 to 4/1 metal ion ratio, at a temperature in the range of about 735 to 825 F. and a hydrogen partial pressure of about 2500 to about 4000 p.s.i.

The present invention relates to the art of petroleum refining or processing and, more particularly, to the production of lubricating oils of high viscosity index. Still more particularly, the present invention is directed to a process for treating a lube oil hydrocracker charge whereby the high viscosity index oils produced have a high quality and are produced in greater yields than heretofore by subjecting separate fractions of a lube oil hydrocracker charge stock to hydrocracking conditions for a time and temperature commensurate with the polyfused-ring aromatics present in the respective separate fraction.

BACKGROUND OF THE INVENTION In the art of petroleum refining, a particularly desired lubricating oil product is one which possesses a multiple viscosity characteristic or alternatively described as a high viscosity index (V.I.) oil in order that the oil will perform at a high degree of efficacy at varying degrees of temperature to which it is subjected in use. There has been an ever-increasing demand for high V.I. oils, and there is a decreasing amount of natural sources from which said oils may be obtained. Accordingly, it is desirous that the industry discover ways of manufacturing these materials from those sources which are available. It is fortuitous for the industry that recent developments in the art of hydrocracking of lube oils (principally catalysts) constitute major technical advances resulting in the hydrocracking technique for the manufacture of high V.I. lube oils, a commercially feasible route to these desired oils. While these developments provide a commercially feasible technique for producing these oils, it is nevertheless not only possible but also desirable to achieve greater efficiencies as well as higher quality of the lube oil so produced. The present discovery provides a desirable and, in fact, commendable improvement in the manufacture of high V.I. oils by hydrocracking.

SUMMARY OF THE INVENTION It has now been found that if a lube oil hydrocracking charge is separated into fractions commensurate with the amount of polyfused-ring aromatics, or if streams suitable for hydrocracking to high V.I. lubes having significant differences in polyfused-ring aromatic content are separately charged to a hydrocracker and each of said streams are subjected to hydrocracking conditions for a time commensurate with the polyfused-ring aromatic content, the yields and quality of the hydrocracked lube product are substantially enhanced.

DETAILED DISCUSSION Typically, lube oil hydrocracking processes use a relatively heavy charge stock containing a large amount of cyclic compounds such as the naphthenes, aromatics, and in most cases polycyclic fused-ring compounds. Typical charge stocks are unpressed vacuum distillates, deasphalted reduced crudes, pressed and unpressed deasphalted residuums, all usually boiling above about 650 F. While not wishing to be bound by any theories set forth herein, it is believed that those theories advanced heretofore by others are correct as to the mechanism involved in hydrocracking enhancement of the V.I. of such lube oil fractions. These theories postulate that the V.I. increase has been in large part due to ring-scission of the polycyclic compounds in said materials, but with minimal cleavage of said compounds into lower molecular weight materials. Notwithstanding the fact that ring-scission plays an important part in the accomplishment of V.I. enhancement, it has been observed that certain types of ring compounds have an apparent adverse effect in the hydrocracking. It is believed that the bad actors responsible for the adverse efifect are some form of polyfused-ring aromatic compound. This conclusion is based in part on the observation that by taking a heavy lube fraction like those typically employed in a hydrocracker and fractionating same, the top or light fraction, although containing substantially the same percentage of aromatics, contains less fused-ring aromatics than the heavier fractions; and this produces a very good hydrocracked lube oil product in very good yields. Unless pretreated, for example, by solvent extraction or deasphalting before hydrocracking, the heavier fractions become progressively worse in term of yields as well as quality of the high V.I. product as the molecular weight, boiling point, and amount of the polyfused-ring aromatics content increase therein.

This can be explained as follows: The hydrocracker feed stock is invariably a complex mixture of compounds as indeed any petroleum fraction is, and the heavier frac tions invariably comprise a mixture of polyfused-ring compounds of various types. Certain of these polyfusedring compounds are easier to break than others. Hydrocracking operating conditions are quite naturally adjusted to the particular feed and based on the results obtained therewith. The greater the amount of hydrocracking refractory materials present, the more operating conditions tend to be adjusted upward, the temperature in particular. In making such adjustments in operating conditions, certainly more of the refractory materials are caused to break and open up into aliphatic substituents on a remaining ring(s). However, at the same time that this occurs, some components in the feed that are more easily hydrocracked (generally the polyfused-ring naphthenics) are overcracked at the more strenuous conditions required and employed to open up greater amounts of the more refractory material in admixture therewith. This overcracked material reduces lube yield because a large portion of it will be too light for inclusion in lube fractions. On the other hand, if the operating conditions are based on the predominant conversion of non-refractory materials present, the refractory materials present will be undercracked and, accordingly, offset the good V.I. material produced by the ring-scission of the non-refractory components. It has been observed that generally the amount of overcracking of the easier-to-crack materials exceeds the amount of ring-opening of the more refractory materials, thereby decreasing the overall yield of desired high V.I lube product in severe operations. Of course, some overcracking results in cleavage of molecules into less valuable low molecular weight products such as gasoline The present invention can be carried out by any one or combination of several embodiments. For example, and preferably, a hydrocracking reactor constructed to provide for a plurality of separate feed conduits at various intermediate points of the catalyst bed(s) of a plurality of serial arranged beds or manifold means for charging separate feeds to different intermediate points of the length of the catalyst bed(s). Beginning with the heaviest unrefined lube oil hydrocracking charge stock which will contain the largest amount of more refractory components, i.e., polyfused-ring aromatics, it is charged at the topmost portion of the bed(s) so that the more refractory components travel the full length of the catalyst bed(s), thereby receiving the longest exposure to hydrocracking conditions. Then, as each next adjacent fraction of feed contains progressively less refractory components, it is charged at a progressively lower point on the catalyst bed(s) so that the fraction containing the least refractory component travels the shortest length of the catalyst bed(s) and is exposed to hydrocracking conditions for the shortest time. Feed fractions containing an intermediate amount of more refractory materials are to be passed over an intermediate length of the catalyst bed(s) and thereby are exposed to hydrocracking conditions for an intermediate amount of time commensurate with its refractory content. As a practical matter, the fraction boiling above about 1000 F. is deasphalted, and after deasphalting it no longer contains as much polycyclics as the preceding fraction and treatment is varied accordingly. In lieu of a longer residence time, the fractions containing larger amounts of polycyclics may be treated at higher temperatures to bring about suflicient cracking of the more refractory materials.

While theoretically there is no limit to the number of fractions and corresponding inlets to the bed(s), there is, of course, a practical limit dictated primarily by economics. In the case of a residuum of relatively broad spectrum or similar hydrocracking charge, i.e., a charge containing all material boiling above about 650 F. (with the exception, of course, of the metals, asphaltenes, etc., convenitionally removed by deasphalting from fractions requiring that operation), the feed should be separated into at least about three feed fractions and charged at at least two points along the catalyst bed(s). As is readily apparent from the foregoing, some fractions can be combined and charged together. For example, in the simplest and generally preferred case, the lub stock is separated into three fractions: the first fraction boiling in the range of about 650 to 875 F., but preferably about 700 to 850 F.; the second fraction boiling in the range of about 850 to l000 F and the third fraction containing all of the material which has been deasphalted boiling at about 1000 F. and above. It is to be fully appreciated in stating the foregoing temperature limits of the fractions that they are capable of some variation depending on several factors; however, the 100 F. cut point for the deasphalter is especially subject to variation by a substantial number of degrees. Normally, the minimum boiling material charged to a deasphalter is about 1000 F., but the precise cut point is determined by economic considerations based on the fact that dcasphalting is an expense which is, if it can, to be avoided. On the other hand, the particular crudes character and especially the efiiciency or efiicacy of the vacuum tower are perhaps even more important. Deasphalting, as those skilled in the art are well aware, is carried out to remove metals, asphaltens, resins, and other undesired materials before further processing them under conditions in which they exert an adverse effect. Accordingly, the approximate 1000 F. limitation on the deasphalted fraction and the preceding fraction is to be viewed in light of this wellknow technology.

The catalyst composition may be the same or different in the several beds or zones of a single bed with the composition selected dependent on the charge stock to be passed over same and the known characteristics of the particular catalyst composition. Any lube oil hydrocracking catalyst suitable for the manufacture of high V.I. lubes can be employed; however, generally preferred catalysts are sulfides of a Group VI metal, lefthancl column, of the periodic system, mixed with an iron group metal. Most preferably, the catalyst is a mixture of nickel sulfide and tungsten sulfide in a l/1 to 4/1 metal ion ratio.

The temperatures employed can be the same throughout the bed(s) or different but, in general, will be in the range of about 650 to 875 F., more usually and preferably in the range of about 735 to 925 F.

The partial pressure of hydrogen should be at least about 1500 psi. and more usually above about 2500 psi. to about 4000 psi, although hydrogen partial pressures as high as about 10,000 psi can be employed. If adequate provisions are taken in constructing the equipment, the pressure can be varied in the various catalyst beds. Operating with different pressures in the different catalyst beds is more easily accomplished in either a blockedout operation or by using a plurality of parallel reactors wherein the various feed fractions are separately charged and the products separately recovered.

In an operation wherein a plurality of catalysts beds in series are employed or a single long catalyst bed is employed with intermediate feed inlets, provision will need to be made in reactor design for the increasing volume of material being processed in the latter stages. This, of course, can be compensated for in several ways, such as by increasing the length and/ or diameter of the reactor commensurate with the increased volume to be hydrocracked.

It is to be understood here that the reaction variables are interdependent, and particularly temperature and resi deuce time, or as it is more frequently stated, the flow rates. This has particular significance in a blocked-out or other operation Where completely separate reactors are employed. Because of the possibilities presented by a blocked-out operation, parallel reactors, or other means of processing fractions completely separately, such embodiments are not to be regarded as full equivalents although certainly there is some functional equivalence.

To be more specific, temperature and residence time vary inversely on a particular oil charge if substantially equivalent results are to be obtained. As the temperature is increased, the residence time is to be decreased by increasing the flow rates if substantially equivalent results are to be obtained. Of course, those skilled in the art can appreciate that temperature accelerates cracking rates exponentially so that as the temperature is increased to the higher ranges a greater incremental change is required in the residence time to offset its effect than in the lower ranges. Also, at the higher temperatures a product of higher aromaticity is sometimes produced with all other properties being substantially the same. This is because of an apparent hydrogenation-dehydrogenation equilibrium which is reached in the higher ranges of temperature. It is with the foregoing qualifications understood that the discussions above and below have equated temperature and residence time on an inverse effect basis.

The interplay of reaction temperature and residence time (or space rate) has considerably more commercial importance when properly applied to two diflFerent charge fractions in a blocked-out or parallel reactor embodiment if the product streams of the different fractions are not mixed as they are in the case of serially arranged reactors. This is because the heavier fractions which contain more refractory materials are subjected to more vigorous conditions, which invariably results in more cracking of heavier molecules to lower molecular weight compounds. This is true whether the more vigorous conditions consist of an increased temperature or longer reaction time or a combination of the two. While the more vigirous conditions produce a portion of the fraction which has a substantially unchanged high molecular weight and an upgraded high V.I., another portion of product from that same fraction has a relatively lower molecular weight from cleavagecracking and a relatively low V.I. A substantial amount of this lower molecular weight material has a molecular weight and boiling point similar to the desired high V.I. upgraded uncleaved product from charging a lighter distillate fraction of the crude and processing it at milder conditions. Unless a blocked-out operation or parallel reactor embodiment is employed, this low molecular weight and low V.I. product obtained from the heavy, more refractory material is recovered in admixture with the material of a similar molecular weight and high V.I. from a lighter charge fraction. This, of course, produces an inseparable blend of light material having a composite V.I. in between that of the low V.I. cleavage product and that of the high V.I. product from the lighter charge fraction. The composite V.I. of the blend may be so low as to require rerunning the blend to upgrade the V.I., and in any event the blend has a substantially lowered V.I. as compared to the high V.I. product from the lighter charge. In a blocked-out or parallel reactor embodiment, these materials can be recovered separately and the low V.I. material from cleavage-cracking of the heavier fraction alone can, if desired, be rerun to increase its V.I. Alternatively, the low V.I. material may be sold separately by the refiner for uses commensurate with its properties and the high V.I. material recovered and obtained and sold as a high V.I. lube oil blending stock. There is, of course, always some sacrifice in yieldat the expense of increase in V.I. in any hydrocarcking operation because of cleavagecracking. However, in the blocked-out or parallel arrangement embodiments of the present invention, considerable flexibility in terms of product distribution of desired viscosity stocks with a high V.I. is provided by reason of the cleavage-cracking phenomena. This is achieved in several ways; for example, any fraction present in excess can be reduced in amount by adjusting process conditions or rerunning it in a fashion commensurate with its refractory character to reduce its yield by cleavage-cracking and thereby produce a corresponding amount of lower molecular weight product with a relatively low V.I. The lower molecular weight product then can be upgraded to a higher V.I. by rerunning at conditions which are more favorable to upgrading than cleavage-cracking. Any rerunning can be conveniently carried out by recycle of material in a continuous operation. The foregoing discussed dilferences can be better understood upon reading the illustrative examples and the product distribution aspect in particular from Illustrative Example II.

ILLUSTRATIVE EXAMPLE I To provide a fuller understanding of the invention, a detailed example with reference to the diagrammatic illustration found in FIG. 1 will now be set forth. A suitable hydrocracking charge residuum boiling above about 650 F. is split into three fractions and placed in separate reservoirs. In Rerservoir No. 1 is placed the material boiling in the range of about 650 to 850 F. In Reservoir No. 2 is placed the material boiling in the range of about 850 to 1000 F. In Reservoir No. 3 is placed the ma- 6 terial boiling at about 1000 F. and above including asphaltenes, and the like, normally present in such heavy fractions.

The material from Reservoir No. 3 is first charged via line 3 to deasphalter 4, and the deasphalted product is charged via line 5 to connecting conduit 9 and into Hydrocracker No. 2 which is the middle reactor of three serially arranged hydrocracking reactors. This reactor (and all the other hydrocracking reactors described hereinafter) contains a catalyst bed comprising a nickel sulfide-tungsten sulfide mixture (in a metals ratio of about 4/1 respectively) on alumina carrier. The temperature is maintained at about 770 F. and a hydrogen partial pressure is maintained at about 2500 p.s.i. (g.), the latter being maintained by hydrogen additions through line 7.

The material from Reservoir No. 2 is charged via line 2. to the first hydrocracker, Hydrocracker No. 33, wherein the temperature is maintained at about 770 F. and the partial pressure of hydrogen is maintained at about 2500 p.s.i.(g.) by the addition of hydrogen via line 7. The feed fraction charged is passed over a catalyst similar to that in Hydrocracker No. 2 at the foregoing conditions; and the reactor effluent is charged via connecting conduit 9 to Hydrocracker No. 2, admixed with deasphalted oil from Reservoir No. 3, and processed therewith.

The material from Reservoir No. 1 is charged via line 1 to connecting conduit 10, admixed therein with the effluent from Hydrocracker No. 2, and passed over a nickel sulfide-tungsten sulfide catalyst at a temperature of about 750 F and a partial pressure of hydrogen of about 2500 p.s.i. (g.) maintained by the addition of hydrogen through line 6. The effluent from Hydrocracker No. 1 is passed via line 11 to a fractionating tower 12 where the gases and other very light materials are separated and the hydrocracked oil is fractionated into Neutral, 200 Neutral, 500 Neutral, and Bright stock fractions of typical respective viscosities but of high V.I.s on the order of to 116.

ILLUSTRATIVE EXAMPLE II To provide a fuller understanding of the parallel reactor embodiment and the shifting of product distribution by recycle, a detailed example with reference to the diagrammatic illustration found in FIG. 2 Will now be set forth. As in Example I, a suitable hydrocracking charge residuum boiling above about 650 F. is spit into three fractions and placed in separate reservoirs. In Reservoir No. 1 is placed the material boiling in the range of about 650 to 850 F. In Reservoir No. 2 is placed the material boiling in the range of about 850 to 1000 F. In Reservoir No. 3 is placed the material boiling at about 1000 F. and above including asphaltenes, and the like, normally present in such heavy fractions.

The material from Reservoir No. 3- is first charged via line 3 to deasphalter 4, and the deasphalted product is charged via line 5 to Hydrocracker No. L2 which is one of three separate hydrocrackers. This reactor (and all the other hydrocracking reactors hereinafter described) contains a catalyst bed comprising a nickel sulfidetungsten sulfide mixture (in a metals ratio of about 4/1 respectively) on alumina carrier. The temperature is maintained at about 755 F. and hydrogen partial pressure is maintained at about 2500 p.s.i.g., the latter being maintained by hydrogen additions through line 6. The efiluent from Hydrocracker No. 2 is charged to Fractionator No. 2 via line 7 where the products of the hydrocracking are fractionated into four fractions, i.e., 100 Neutral, 200 Neutral, 500 Neutral, and Bright Stock. The lighter material approximating 100 Neutral with a V.I. of about 85 is charged via line 8 to line 1 which is the feed line to Hydrocracker No. 1 for V.I. upgrading. This latter feature warrants some cautionary comments. Admixing the light material from Hydrocracker No. 2 will frequently produce a material having a lower V.I. than that of material from Reservoir No. 1 and will result in a blend 7 having a lower composite V.I. than the product from Reservoir No. 1 alone. Accordingly, in some cases the operator will find it preferable to recover the material in line 8 and dispose of it in some other fashion. Gases and very light materials are then taken off through line 9.

The material from Reservoir No. 1 is charged via line 1 to separate Hydrocracker No. 1 and is admixed in line 1 with the separated light fraction of the eflluent from Hydrocracker No. 2 and is passed over a catalyst similar to that in Hydrocracker No. 2 at a temperature of about 748 F. and a partial pressure of hydrogen of about 2500 p.s.i.g. maintained by the addition of hydrogen through line 10. The efiiuent from Hydrocracker No. 1 is passed via line 11 to Fractionator No. 1, where the gases and other very light materials are separated and taken oif through line 12 and the hydrocracked oil is fractionated into a very light fraction too light for a lube oil blending stock and into a heavier fraction having the typical boiling point and viscosity of a 100 Neutral oil but having a high V.I. on the order of 105, making it highly suitable as a high V.'I. lube oil blending stock. A small amount of 200 Neutral at 115 V1. is also formed and recovered here.

The material from Reservoir No. 2 is charged via line 2 to separate Hydrocracker No. 3, wherein the temperature is maintained at about 755 F. and the partial pressure of hydrogen is maintained at about 2500 p.s.i.g. by the addition of hydrogen via line 13, and is passed over a catalyst similar to that in Hydrocracker No. 2. The reactor effluent is charged via line 14 to Fractionator No. 3 where it is fractionated into a light fraction similar in boiling point and viscosity to the deasphalted residuum charged to Hydrocracker No. 2, and this material is charged via line 15 to feed line and then into Hydrocracker No. 2 for upgrading in V.I. The effiuent from Hydrocracker No. 3 is also fractionated into a fraction which has typical boiling points and viscosities of a No. 2 and No. 4 distillate, both of which are highly suitable as high V.I. lube stocks.

In the example immediately above, the results there are obtained using a space velocity (i.e., liquid volumes of feed per volume of catalyst per hour) of about 0.5 in all three hydrocrackers. However, the space velocity can vary considerably but usually will be in the range of about 0.1 to 4. In most cases, it is preferably to operate at space velocities in the range of about 0.25 to 1.5.

What is claimed is:

1. A process of hydrocracking lube oil stocks to high viscosity index oils comprising fractionating a lube oil charge stock boiling above about 650 F. into a plurality of fractions having different boiling ranges, subjecting a higher boiling fraction to hydrocracking conditions of from 650 to 875 F. under a hydrogen partial pressure of at least about 1500 p.s.i. in the presence of a hydrocracking catalyst and comibning this hydrocracked higher boiling fraction with a lower boiling fraction and subjecting the thus formed mixture to hydrocracking conditions of from 650 F. to 875 F. under a hydrogen partial pressure of at least 1500 p.s.i.

2. The process of claim 1 wherein the lube oil charge stock is an unpressed vacuum distillate, a deasphalted reduced crude, a pressed deasphalted residuum, an unpressed deasphalted residuum, or blend-s thereof.

3. The process of claim 2 wherein the charge stock is fractionated into three fractions boiling in the ranges of about 650 F. to about 850 F., about 850 F. to about 1000 F., and above about 1000 F., wherein the fraction boiling above 1000 F. is deasphalted, and wherein the fraction boiling from about 850 F. to about 1000 F. after being subjected to hydrocracking conditions is combined with at least a portion of the deasphalted fraction boiling above about 1000 F. which mixture is further subjected to hydrocracking conditions.

4. The process of claim 3 wherein partial pressure of hydrogen of from about 2500 to about 4000 p.s.i. is used in all of the hydrocracking steps.

5. The process of claim 4 wherein a temperature of from about 735 F. to about 825 F. is used in all of the hydrocracking steps.

6. The process of claim 5 wherein at least a portion of the fraction boiling at from about 650 F. to about 850 F. is combined with the combined hydrocracked fractions boiling at from about 850 F. to about 1000 F. and at above about 1000 F. and the mixture further subjected to hydrocracking conditions.

7. The process of claim 4 wherein the charge stock is fractionated into three fractions boiling in the ranges of about 650 F. to about 850 F., 850 F. to about 1000 F. and above about 1000 F., deasphalting the fraction boiling above about 1000 F., separately subjecting the fractions to hydrocracking conditions of from about 650 F. to 875 F. and a hydrogen partial pressure of at least about 1500 p.s.i. wherein the fraction boiling at from about 850 F. to about 1000 F. is more severely hydrocracked, and combining at least a portion of each of the hydrocracked fractions to form a high viscosity lube oil.

8. The process of claim 7 wherein a partial pressure of hydrogen of from about 2500 to about 4000 p.s.i. is used in all of the hydrocracking steps.

9. The process of claim 8 wherein a temperature of from about 735 F. to about 825 F. is used in all of the hydrocracking steps.

References Cited UNITED STATES PATENTS 2,787,582 4/1957 Watkins et a1. 20858 3,242,068 3/1966 Paterson 208-18 3,256,175 6/1966 Kozlowski et a1. 20892 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 208-l9, 93 

